Casting apparatus for encapsulating electrical conductors



S p 2231979 I v amqgsnus ETAL 3,529,320 I CASTING APPARATUS FORENCAPSULATING ELECTRICAL CONDUCTORS Filed Oct. 17, 1967 5 Sheets-Snuet 1CONTROL WITNESSES INVE NTORS v I Bernard A. Kerns.Lowrence J. Manningand Alexander Toleff BY $9 Giif? Sept. 22, 1910 I B. A. KERNS mL 3.59320 CASTING APPARATUS FOR ENCAPSULATING ELECTRICAL CONDUCTOBS Filed001:. 17, 1967 5 Sheets-Sheet 2 FIG. 2.

VACUUM SYSTEM TO COMPRESSOR I68 TO I62 AUXILIARY SYSTEM I l0 TO CENTRALVACUUM SYSTEM Sept 22, 1910 B. A. KERNS F-TAL CASTING APPARATUS FOR;ENCAPSULATING ELECTRICAL CONSUCTORS Filed ()Glt. 17, 1967 HOLDINGTRANSFER STEP STEP

' POURING MAIN VACUUM STEP CHAMBER SYSTEM 3 Sheets-Sheet :5

AUXILIARY VACUUM SYSTEM EVACUATING STEP LOADING STEP DEGASSING UNLOADING-2|s STEP STEP BLEEDING 250 STEP CURING "2'6 STEP 2a 7 I I I 234:HEATING 232 MIXING AND MEANS DISPENSING MEANS 236 230 FIG. 3.

MATERIALS FOR 240 RESIN SYSTEM 242 VACUUM United States Patent Oflice3,529,320 CASTING APPARATUS FOR ENCAPSULATING ELECTRICAL CONDUCTORSBernard A. Kerns, Lawrence J. Manning, and Alexander Taletf, Pittsburgh,Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., acorporation of Pennsylvania Filed Oct. 17, 1967, Ser. No. 675,841

Int. Cl. B26c 6/00 US. Cl. 18--5 Claims ABSTRACT OF THE DISCLOSURECasting apparatus for at least partially encapsulating electricallyconductive means in an insulating resin system. The casting machine orapparatus includes a rotary carriage which supports a plurality ofvacuum chambers, and drive means for indexing the carriage. The castingmachine includes first and second separate vacuum systems, the first ofwhich is connectable to the vacuum chambers at one of the machine indexpositions to provide the initial vacuum, and the other of which ispermanently connected to each vacuum chamber through a rotary shaftseal, and an individual valve for each vacuum chamber. After thepressure in a vaccum chamber is reduced by the first vacuum system to amagnitude which is substantialy the same as that of the second vacuumsystem, the first vacuum system is disconected from the vacuum chamber,and the valve is opened to the second vacuum system, thus transferringeach vacuum chamber from the first vacuum system to the second vacuumsystem. Also included is means for sealably introducing a pourable castresin system into a vacuum chamber and its mold, and valve means forreturning each vacuum chamber to atmospheric pressure after the vacuumpouring and degassing steps are completed.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesto apparatus for at least partially encapsulating electrical conductors,such as coils, windings, and electrical bushing conductor studs, with apourable cast resinous solid insulation system.

Description of the prior art Prior art encapsulating methods andapparatus generally operate on the batch principle, wherein molds areintroduced into a vacuum chamber, the vacuum chamber is evacuated, theresin system is poured, the chamber is brought back to atmosphericpressure, and the filled molds are removed. While this method andapparatus produces acceptable encapsulated electrical devices,production capabilities are limited due to the length of time requiredfor the various steps of the process. Increasing the number of batchoperations to provide the required production rate is not an economicalsolution, as it is very costly due to the duplication of apparatus, andit requires a large number of operating personnel, as well as extensivefloor space. It would be more desirable to provide new and improvedapparatus for encapsulating electrical conductors, which substantiallyincreases the production capability of the apparatus, compared withbatch type methods, without a correspoding increase in cost, floor spaceand operating personnel.

SUMMARY OF THE INVENTION Briefly, the invention discloses new andimproved apparatus for casting pourable resin systems, which includes arotatable carriage having a plurality of vacuum chambers disposedthereon, and drive means for rotating the carriage between predeterminedindex positions. Each vacuum chamber has a scalable opening adapted forreceiving molds, and each vacuum chamber is connected to a centralvacuum system by virtue of a rotating shaft seal which allows the vacuumto be brought to a central manifold on the rotatable carriage. Suitablevalved piping means from the manifold to each vacuum chamber completethe central vacuum system. Each vacuum chamber also includes a valvewhich cooperates with an auxiliary vacuum system at one of the indexpositions, in order to evacuate the vacuum chambers and allow eachvacuum chamber to enter the central vacuum system already at the samepressure as the central vacuum system. This valve also cooperates withmeans for sealingly introducing a resin system into the vacuum chamberand its molds. Another valve is also included on each vacuum chamber forbleeding air into the chambers to return them to atmospheric pressureafter the manufacturing steps which require a vacuum have beencompleted.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of theinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIG. 1 is a plan view of a casting machine or apparatus constructedaccording to the teachings of the invention;

FIG. 2 is an elevational sectional view of the casting apparatus shownin FIG. 1, with the section being taken generally along the lines IIIIof FIG. 1; and

FIG. 3 is a process flow diagram illustrating a method for castingelectrical conductors in accordance with the teachings of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,and FIGS. 1 and 2 in particular, there is shown plan and elevationalviews, respectively, of new and improved casting apparatus 10constructed according to the teachings of the invention. In order tomore clearly illustrate the construction of the casting apparatus 10,the elevational view in FIG. 2 is a section taken generally along thelines II--Il of FIG. 1. In general, casting apparatus or machine 10comprises a rotatable carriage 12, a supporting base 14, drive means 16for indexing the rotatable carriage 12, a plurality of vacuum chambers18, 20, 22, 24, 26, 28, 30 and 32 disposed in spaced relation on thecarriage 12, a central vacuum system distributable to the various vacuumcham-- bers through manifold means 34, means 36 connectable to thevacuum chambers for providing an initial vacuum in the vacuum chambers,means 38 for mixing and storing the components of the resin system, anddispensing means 40 for metering and dispensing the resin system intothe vacuum chambers at the proper time.

Supporting base 14 may be of any suitable construction, for example,having a structural steel bed 42 which is elevated and supported by aplurality of steel leg members 44. A plurality of upstanding rollermembers 46 are disposed on bed 42, equally spaced about thecircumference of a predetermined circle for supporting and allowingrotary movement of the carriage 12.

Carriage 12 is a substantially circular wheel or spiderlike structure,having a steel tubular inner member 48 which forms the hub of the wheel,and a plurality of radially extending web portions 50 which are weldedto the tubular member 48. The supporting members for the vacuumchambers, such as vacuum chamber 18, are formed by welding steel channelmembers between the plurality of webs 50, to form two spaced,concentric, substantially ring-shaped supporting members 52 and 54.

Supporting members 52 and 54 are radially spaced to support the mountingfeet of the various vacuum chambers.

Welded to the bottom of the substantially ring-shaped supporting member54 is a cylindrical ring or bearing member 56 which rests on theplurality of upstanding rollers 46 mounted on the bed 42.

The vacuum chambers 18, 20, 22, 24, 26, 28, 30 and 32 each have mountingfeet, such as feet 58 on vacuum chamber 24, which are bolted, orotherwise suitably fixed to support members 52 and 54, with the vacuumchambers being equally spaced about the perimeter of supporting members52 and 54.

The vacuum manifold 34 for distributing the vacuum from the main vacuumsystem (not shown) has a circumferential flange which is bolted to awasher-like plate member 60, with member 60 being welded to the upperend of the inner tubular member 48. Manifold 34 extends downwardlythrough the washer-like member 60, into the central opening of the innertubular member 48, and has a downwardly extending pipe member or conduit62 which is in communication with the inside of the manifold 34. Conduit62 is fixed and sealed to a rotary portion 66 of shaft seal assembly 64,which performs the functions of radially guiding the carriage assembly12 and connecting the stationary central vacuum system with therotatable manifold 34. The central vacuum system is connected to thestationary portion 68 of the shaft seal assembly 64 via conduit orpiping means 70. A suitable tubular shaft seal 72 is mounted on theinternal surface of the stationary portion 68 of shaft seal assembly 64,and has an inside diameter which snugly fits the rotatable portion 66 ofthe shaft seal, allowing the portion 66 to rotate, but sealing the shaftagainst air leakage into the vacuum system. Suitable radial bearings(not shown) are disposed at both ends of the shaft seal 72 in order toguide the carriage 12 when it is being rotated.

The vacuum manifold 34 is connected to vacuum chambers 18, 20, 22, 24,26, 28-, 30 and 32 through radially extending conduit means 74, 76, 78,80, 82, 84, 86 and 88, respectively, and each conduit means includes anelectrically operated valve for operatively connecting or disconnectingeach vacuum chamber with the vacuum manifold 34, such as valves 90, 92,94, 96, 98, 100, 102 and 104, respectively. Thus, each vacuum chambermay be individually and selectively connected to the vacuum manifold 34and thus to the central vacuum system through its associatedelectrically operated valve.

Rotatable carriage means 12 is indexed by drive means 16, which includesair or hydraulically operated cylinder means which successively engage aplurality of spaced pins on the carriage 12, such as pin 106, to movethe vacuum chambers through a plurality of index positions. Since inthis embodiment of the invention there are eight vacuum chambers, eachindex of the drive means 16 will be arranged to rotate the carriage 45degrees. The various processing steps for encapsulating the electricalconductors in solid resinous insulation are performed at various indexpositions, as will be hereinafter explained.

Each of the vacuum chambers 18, 20, 22, 24, 26, 28, 30 and 32 aresimilar in construction, having a vacuum chamber formed by asubstantially cylindrical housing 108 which has its axis horizontallydisposed, with housing 108 having an open end which faces radiallyoutward for receiving the mold which is to be filled with the resinsystem, such as the mold 110 shown in vacuum chamber 18. Vacuum chamber18 is shown partially cut away in FIG. 1 to illustrate the mold 110 andthe support rails 112 for holding the mold 110 in the vacuum chamber.

The open end of housing 108 is closed by a door 114, which is sealed byturning a locking ring 11 6. Looking ring 116 may be automaticallyactuated by an air cylinder, such as cylinder 118, and the door 114 maybe opened and closed by an air cylinder, such as cylinder 120.

The vacuum chamber may be heated by a plurality of heaters at certaintimes during the processing cycle, such as electrically operated heaters122, shown most clearly on vacuum chamber 18 in FIG. 1. However, in mostapplications auxiliary heat is not required, and heat transfer throughthe vacuum is so poor that very little heat is lost from the initiallyheated electrical conductor to be encapsulated, and from the heatedresin system once it is poured.

Each vacuum chamber also has two valves, a gate valve 126, mounted onthe top of the housing 108, and a bleed valve 128 mounted at anyconvenient location on the housing 108. The gate valve 126, which may beoperated by an air cylinder, has a flat upper plate 130 which has asuitable opening therein, with a groove and O-ring combinationsurrounding the opening such that the O-ring extends slightly above thesurface of the plate 130'. Thus, as will be hereinafter explained, whenaccess to the internal portion of the vacuum chamber is to be obtainedthrough the gate valve 126, the opening of the gate valve may be sealedby a flat plate pressed against the plate 130 and its sealing O-ring.

Bleed valve 128, which may be electrically operated, provides thefunction of bleeding air into the vacuum chamber after it has beeneffectively disconnected from the vacuum manifold 34 by its associatedmain or central vacuum system valve, such as valve 96 associated withvacuum chamber 24, when it is desired to return the vacuum chamber toatmospheric pressure, to allow door 114 to be opened and the mold to beremoved therefrom.

The vacuum chamber may also include a light disposed within housing 108,such as light 132 shown in vacuum chamber 30 in FIG. 2, and a sight port134 which allows visual inspection by an operator such as during thefilling of the mold 110 with the resinous insulating system. A vacuumgauge 129 may also be disposed on the outside of each vacuum chamber sothat an operator can readily determine the condition of the vacuum inthe chamber.

In addition to continuously providing a vacuum to the rotatable carriage12 from a stationary central vacuum system, it is also necessary toprovide electrical power to the carriage 12 for the operation of thevarious valves, limit switches, lights, control functions, and theelectrical heaters, if used. This is accomplished by a plurality ofconcentrically disposed electrically conductive rings 136, formed of amaterial such as copper, which are insulatingly mounted to the carriage12, and which are accessible from below. Brushes 138 are insulatinglymounted on the stationary bed 42, and disposed to contact the rings 136.Thus, electrical power is transferred through the brushes to the rings,with the source of electrical potential being connected to the brushes138 and the various control functions being connected to the rings 136.

It is also necessary to provide a supply of air to the rotary portion ofthe casting apparatus 10, and this may be provided by an electricallyoperated compressor disposed on the carriage 12, or as shown in FIG. 2it may be provided from a stationary source of air through a I rotaryair seal 69 and air conduit which may enter the carriage 12 along itsvertical axis.

According to the teachings of the invention, each vacuum chamber, suchas vacuum chamber 18, is permanently connected to the central vacuumsystem through individual valves, such as valve 90. A vacuum chambercannot directly enter the central vacuum system while it is itself atatmospheric pressure, however, as it would immediately increase thepressure in all of the vacuum chambers which are operatively connectedto the central vacuum system. Therefore, after loading a mold into avacuum chamber and closing and sealing the door, the vacuum chamber mustbe brought down to substantially the same pressure or vacuum as that ofthe central sys tem, to allow its central system valve to be openedwithout adversely affecting the central vacuum system. This may beconveniently accomplished at the index position which follows theloading position. For convenience, the index positions in FIG. 1 areindicated with Roman numerals I through VIII. Thus, in FIG. 1 if it isassumed that index position I is the load" index position, and the indexrotation is counterclockwise as indicated by arrow 140, then indexposition II is the index position at which the 'vacuum chambers may beinitially evacuated with an auxiliary vacuum system. Accordingly, asshown in FIGS. 1 and 2, means 36 is provided at index position II forevacuating the vacuum chambers, such as vacuum chamber 24, while theyare at this index position. Means 36 includes a conduit 142 which isconnected to the auxiliary vacuum pump (not shown), a valve 144, whichmay be electrically operated, for opening and closing conduit 142 asdesired, a stationary horizontally disposed mounting plate 146 whichcontains a plurality of air cylinders 148 mounted transversely to theplate, and having their operating rods downwardly disposed and connectedto a movable plate member 150 through a flexible bellowslike coupling152. Thus, when vacuum chamber 24 is in index position II, its centralsystem vacuum valve 96 should be closed, and auxiliary vacuum valve 144should be closed. The air cylinders 148 may then be actuated to lowerplate 150, which has an opening therein, against plate 130, with theopening in plate 150 being aligned with the opening in plate 130. TheO-ring on the upper surface of plate 130 will be compressed by plate150, forming a vacuum tight seal. Gate valve 126 on vacuum chamber 24may then be opened, followed by the opening of the auxiliary vacuumvalve 144. When vacuum chamber 24 is evacuated to the desired pressure,which will usually be in the range of 1-5 mm. of mercury, the gate valve126 may be closed, followed by the closing of auxiliary valve 144. Inorder to release the vacuum which will still exist between the twovalves 126 and 144, a bleed valve 154, shown in FIG. 1 is opened beforethe cylinders 148 are actuated to lift the plate 150. As soon as thegate valve 36 on vacuum chamber 24 has closed, following the initialevacuation, the valve 96 to the central vacuum system may be opened.This may be conveniently accomplished with a limit switch upon theindexing of vacuum chamber 24 to index position III. Since the air inthe mold and its contents, i.e., the electrical conductors to beencapsulated, may have entrapped air which was not completely removed bythe auxiliary vacuum system at index position II, the next two indexpositions III and IV, in this embodiment of the invention, are used toallow the central vacuum system to remove as much trapped air aspossible from the vacuum chambers prior to the pouring of the resinsystem, maintaining the vacuum in the range of 1-5 mm. of mercury.

After the vacuum chamber and its contents have been under the vacuum fora sufiicient length of time to insure removal of substantially allentrapped air, the pourable cast resin system may be introduced into thevacuum chamber and its mold (or molds). As shown in FIGS. 1 and 2, thisis accomplished at index position V. The resin system, which has beenmixed under vacuum in mixer 38 and held at a predetermined elevatedtemperature therein, is introduced into the vacuum chamber at indexposition V, using the same gate valve previously used to provide theinitial evacuation. For example, as shown in FIGS. 1 and 2, vacuumchamber 30 is in index position V and the mixer 38 and dispenser 40 aremounted overhead, connected to a sealing arrangement similar to the oneused by the auxiliary vacuum system in making the vacuum tight seal withthe gate valve 126. The dispensing means 40 has its output end connectedthrough an opening in a horizontally disposed mounting plate .156, whichhas air cylinders 158 mounted thereon, with the cylinder rods extendingdownwardly and connected to a plate member 160 which has an openingtherein. The openings in plate members 156 and 160 are sealed andinterconnected by flexible bellows 162. Thus, when it is desired tointroduce the resin system into a vacuum chamber, the air cylinders 158are actuated, to lower plate 160 against plate 130 to compress itsO-ring, and seal the connection between the dispensing means 40 and thevacuum chamber 30. Gate valve 126 may then be opened and dispensingmeans 40 may meter a predetermined amount of the resin system into themold contained under vacuum in the vacuum chamber.

When the desired amount of material is metered into the mold, thedispensing means 40 will close its output end, and gate valve 126 maythen be closed. Before the cylinders 158 are actuated to lift the platemember 160, bleed valve 164 is opened to release the vacuum betweendispensing means 40 and gate valve 126.

The central vacuum system valve is kept open as the carriage 12 isindexed into position VI and while it is in this position, in order toremove any gases from the poured resin which were not removed during thevacuum mixing process.

As the carriage is again indexed, the central vacuum system valve, suchas valve on vacuum chamber 18, closes, and then the bleed valve 128 onthe vacuum chamber is opened to slowly bring the vacuum chamber back toatmospheric pressure. When the carriage is indexed again, the filledmold may be removed at index position VIII, by first actuating cylinder118 to unlock and unseal the door, and by actuating cylinder 120 to openthe door. The mold may then be removed and put through a predeterminedcuring cycle to gell and cure the cast resin system.

A complete cycle of casting machine 10 will now be described startingwith the vacuum chamber 22 at index position I. Index position I, inthis embodiment of the invention, is a load position. Vacuum chamber 22will index into this position with its door 114 open, and with gatevalve 126, bleed valve 128, and central vacuum system valve 94, closed.The mold 110, along with its electrical conductors to be encapsulated,is placed into the vacuum chamber. The loading may be accomplishedautomatically, such as with a hydraulically operated push rod, and thedoor 14 may be automatically closed by cylinder 120, and sealed andlocked by air cylinder 118 being actuated to turn locking ring 116. Themold and the electrically conductive members disposed therein arepre-heated to approximately the temperature at which the resin systemwill be poured, usually in the range of 80 C. to 110 C. The time thatcasting machine 10 will remain at each index position will be determinedby the longest processing step, and this will depend upon the specificapplication. For example, in the encapsulation of transformer coils,such as disclosed in co-pending application Ser. No. 675,840, filed Oct.17, 1967, which application is assigned to the same assignee as thepresent application, in an eight vacuum chamber casting machine thepouring of the resin would usually require the longest time, setting theindex time at approximately two minutes. If the electrical conductors tobe encapsulated require less resin, such as small electrical bushings,then the pouring time, and thus the cycle time, may be substantiallyreduced. Where smaller devices are to be encapsulated, more than onemold may be place n each vacuum chamber, if desired.

After loading in index position I, the carriage 12 is indexed 45 bydrive means 16, bringing vacuum chamber 22 to index position II and tothe initial evacuation step of the process via the auxiliary vacuumsystem. The

gate valve 126 of vacuum chamber 22 will stop directly under theflexible coupling of the auxiliary vacuum system, and air cylinders 148will be automatically actuated to lower plate 150 against plate of thegate valve 126, sealing the connection. The gate valve 126 is thenautomatically opened and valve 144 Will then open to evacuate the vacuumchamber to a predetermined value. After the evacuation of the vacuumchamber, valve 144 will close, gate valve 126 will close, bleed valve154 will open to release the vacuum between valves 126 and 144 and thenit will close, and cylinder 148 will lift plate 150.

Vacuum chamber 22 will then be indexed to position III, and whileindexing, its valve 94 may be automatically opened. For example, it maybe signalled by a microswitch operated by the movement of the carriage.The vacuum in vacuum chamber 22 will be continuously held at both indexpositions III and IV, with no processing at these two positions. Thetime provided by these two vacuum holding stations insures thatsubstantially all air entrapped in the mold and the electricalconductors to be encapsulated will be removed. From index position IV,vacuum chamber 22 will be indexed into position V, which is where thepouring of the resin takes place. As the vacuum chamber is indexed intothis position, the operator may visually check vacuum gauge 129 toinsure that the vacuum is in the proper range for pouring. The pouringstep may be automatic, or the operator may control it manually.Cylinders 158 are actuated to press plate 160 against plate 130 of thegate valve, the O-ring in the face of plate 130 will seal theconnection, gate valve 126 will open, and dispensing means 40 will beactuated to meter a predetermined amount of resin from mixer means 38into the mold. The dispensing means 40 will then close its outlet, gatevalve 126 will close, bleed valve 164 will open to release the vacuumbetween the dispensing means 40 and the gate valve 126 and cylinders 158will lift plate 160 to break the coupling.

Although the resin system is vacuum mixed in mixer 38, as will behereinafter described, it is necessary to degas the poured resin system.Index position VI is used to perform the degassing step. Thus, whenchamber 22 is indexed into position VI, its central vacuum system valve94 will remain open, and entrapped air will continue to be removed fromthe poured resin system for the duration of this index position.

Vacuum chamber 22 will then be indexed into position VII. At thisposition, its central vacuum valve 94 will close and bleed valve 128will open to slowly bring vacuum chamber 22 back to atmosphericpressure. Casting machine will then index vacuum chamber 22 intoposition VIII, where the filled mold or molds may be automatically ormanually removed. Upon indexing into position VIII, cylinder 118 will beactuated to rotate the locking ring 116 and cylinder 120 will beactuated to open the door 114. The filled molds are ready for thespecific cure cycle of the particular resin system used.

The control for logically coordinating the signals from the variouslimit switches, valves cylinders, micro-switches and the like, to insurethat all of the functions at each index position have been performedbefore the drive means 16 indexes the machine to the next position, maybe conventional, and is therefore shown generally at 170.

The mixer 38 is mounted on a suitable structural steel framework 168above the rotatable portion of the casting machine 10, and it includes ahollow tank or body portion 172, which has an opening at its lower endin sealed communication with dispensing means 40, and a top portion 174which seals the upper end of the mixer tank 172. The mixer tank 172includes relatively large low speed mixer blades (not shown) andsmaller, high speed mixer blades (not shown) driven by co-axial driveshafts disposed vertically through the top portion 174. The high speeddrive shaft is coupled directly to motor 176 via coupling 178, and lowspeed drive shaft is connected to motor 180 through a reduction gear182.

Any suitable castable resin system may be used to encapsulate theelectrical conductors, such as those of the thermoplastic, orthermosetting types. For purposes of example, however, it will beassumed that the resin system is thermosetting and of the epoxy type.Co-pending application Ser. No. 456,038, filed May 6, 1965, nowabandoned, discloses an excellent epoxy resin system that may be used,including an epoxy resin system having an epoxy equivalent weight ofabout 150-450, an anhydride resin curing agent, a resin curingaccelerator, and powdered beryl as the filler. A suitable thixotropicagent may also be added to prevent settling of the filler system. Otherexcellent epoxy resin systems which may be used are disclosed inapplications Ser. Nos. 447,237, now abandoned, and 645,319, now US. Pat.3,433,893, filed Apr. 12, 1965 and June 12, 1967, respectively, with allof these co-pending applications being assigned to the same assignee asthe present application.

A sealable port or opening 184 is shown in FIGS. 1 and 2 for introducingthe components of the resin system, but it is to be understood that thecomponents may be automatically metered and/or weighed and automaticallyintroduced in the mixer 38, if desired. The epoxy resin, its curingagent, and accelerator, are all pre-heated to a predeterminedtemperature, such as between C. to C., at which temperature they arefluid, and they may be accurately metered and pumped into the mixertank. The filler and any thioxtropic agent, if used, will be solid, andmay be automatically weighed and transferred to the mixer tank 172through a sealable opening or openings.

Mixer 38, as shown, mixes all of the components of the resin system,thus providing a predetermined limited period of time in which the resinsystem must be used. It would be equally suitable to divide the resinsystem into two parts, in which the epoxy resin and its curing agent areseparated. Each part would be completely mixed and held in a heatedtank, and they would only be mixed together when required. Therefore,the two portions of the system may be held indefinitely, and only mixedwhen required by the casting machine.

Since the components of the resin system must be mixed and held at apredetermined elevated temperature, the mixer tank 172 may containheating passages through which a heated liquid, such as ethylene glycol,may be circulated. Pipes 186 and 188 indicate the entrance and exit endsof the passages through the jacket of the mixer tank, respectively.

It is essential that the components of the resin system be at leastmixed while under a vacuum, such as a vacuum of 1-5 mm. of mercury, inorder to facilitate the removal of as much air as possible from thesystem before pouring. If the resin system is not outgassed prior topouring in the vacuum chamber, splattering of the resin system willoccur when it is poured into the evacuated chamber. Pipe 190 indicatesthe connection of a vacuum system to the mixer tank 172. This vacuumsystem may be a separate vacuum system, or the auxiliary vacuum systemused to provide the initial evacuation of the vacuum chambers may beused.

After mixing the components of the resin system in mixer 38, the mixedresin system may be held under vacuum; or the mixing chamber may bebrought back to atmospheric pressure. Once the system is mixed undervacuum, it may be returned to atmospheric pressure and it will absorbvery little air. The disadvantage of the system entrapping a smallamount of air after mixing, may be offset by the easier transfer of theresin system from the tank 172 to the molds in the vacuum chambers, whenthe mixing chamber is at atmospheric pressure.

When the mixed resin system in tank 172 has been completely used, thetank may be cleaned before mixing the next batch of resin. Pipe 192 isfor connection to a supply of a suitable cleaning fluid, such astrichloroethylene.

Dispensing means 40 may be a motor and pump combination which will pumpand meter the resin system from the tank 172 when it is desired to filla mold.

FIGS. 1 and 2 illustrate a new and improved casting machine forencapsulating electrical devices in a pourable resin system, accordingto a new and improved method of substantially continuous casting, whichgreatly increases the production rate over prior art methods, whilereducing the required number of operating personnel. FIG. 3 is a flowdiagram which illustrates this method, characterized by the use of arotary vacuum machine, which utilizes two independent vacuum systems.The flow diagram is shown with general reference to the casting machineshown in FIGS. 1 and 2 in order to illustrate the basic steps of themethod and how the casting machine 10 could be arranged to form otherembodiments within the scope of the invention.

The first step of the casting method, illustrated by block 200, is theloading of a mold into a vacuum chamber of a rotary casting machinehaving a plurality of vacuum chambers. The next step of the method,illustrated by block 202, is the evacuation of the vacuum chamber by afirst or auxiliary vacuum system, illustrated by line 219 and circle203. The next step is the transferring of the vauuum chamber from thefirst vacuum system 203 to a second or main vacuum system, indicated bythe line 220 and circle 205. The next step is the holding of the vacuumchamber at a predetermined vacuum, illustrated by block 206 and line221. Since the transferring and holding steps may be combined into oneoperation, instead of using two independent index positions of therotary vacuum casting machine, steps 204 and 206 are shown jointed by adotted line 209. In other words, instead of having two index positionson the casting machine 10 between the evacuating step and the pouringstep, it would be entirely practical to utilize only one index position.The time that the electrical conductors to be encapsulated are undervacuum before pouring is determined by the application, as the longerthe time under vacuum, the less chance there will be of insulationfailure due to air bubbles in the insulation. The next step is thevacuum pouring of the resin system, indicated by block 208 and line 222.The next step is the degassing step, indicated by block 210 and line223, for removing entrapped air from the poured resin system. The nextstep is the bleeding step, indicated by block 212, during which thevacuum chamber is brought back to atmospheric pressure. The next step isthe unloading of the mold from the vacuum chamber, indicated by block214. Since the loading and unloading of the mold may occur at the sameindex position of the rotary casting machine, the unloading and loadingsteps 214 and 200 are shown joined by dotted line 215. The filled moldsare then ready for the curing step, indicated by block 216.

The resin system may be prepared by providing the materials which are tobe combined into the resin system, indicated by block 230, heatingcertain of the materials to a predetermined elevated temperature, withsuitable heating means illustrated by block 232 and line 234,introducing the material into the mixing and dispensing means,illustrated by lines 236 and block 238, mixing the materials undervacuum, illustrated by line 240 and circle 242, heating the mixedmaterials, indicated by line 231 and block 232, and dispensing the mixedsystem to initiate the pouring step 208, indicated by line 250.

In summary, there has been disclosed a new and improved method ofsubstantially continuously casting a pourable resin system aboutelectrical conductors, such as electrical windings, in a rotary vacuumcasting machine which utilizes two separate vacuum systems. The methodincludes the steps of loading a mold which contains the electricalconductors to be encapsulated in a vacuum chamber, evacuating the vacuumchamber with a first vacuum system, transferring the vacuum chamber to asecond vacuum system, pouring a resin into the mold while the vacuumchamber is connected to the second vacuum system, degassing the pouredresin with the second vacuum system, bleeding air into the vacuumchamber to bring it back to atmospheric pressure, unloading the filledmolds from the vacuum chambers, and curing the resin system.

Also disclosed is a new and improved rotary casting machine having aplurality of vacuum chambers, which is suitable for performing the stepsof the new casting method. The machine indexes through a plurality ofpredetermined index positions, performing the different manufacturingsteps at predetermined index positions, which allows one machine and oneoperator to produce encapsulated electrical devices at rates onlyachievable in prior art by utilizing a plurality of separate castingmachines and a plurality of operators.

Since numerous changes may be made in the above described apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all matter contained in theforegoing description or shown in the accompanying drawings, shall beinterpreted as illustrative, and not in a limiting sense.

We claim as our invention:

1. A casting machine for at least partially encapsulating electricallyconductive means in a resin system, comprising:

movable support means,

a plurality of vacuum chambers disposed on said movable support means,said vacuum chambers each having a scalable opening adapted forreceiving at least one mold which contains the electrically conductivemeans to be encapsulated,

drive means for indexing said movable support means to move said vacuumchambers successively through a plurality of index positions,

first vacuum means connectable to a vacuum chamber at one of said indexpositions, for providing a vacuum in the vacuum chamber after a mold isintroduced therein,

second vacuum means,

first valve means connecting each of said plurality of vacuum chambersto said second vacuum means, said first valve means operably connectingcertain of said vacuum chambers to said second vacuum system to maintainthe vacuum provided by said first vacuum means,

means for sealingly introducing a resin system into a vacuum chamber atan index position at which the vacuum chamber is operatively connectedto said second vacuum means, for filling the mold, and

means for bringing the vacuum chamber back to atmospheric pressure, toallow filled molds to be removed from the sealable openings in thevacuum chambers at one of the index positions.

2. The casting machine of claim 1 wherein the movable support is arotatable carriage and including a rotary shaft vacuum seal, wherein theplurality of vacuum chambers are connected to the second vacuum meansthrough the rotary shaft seal.

3. The casting machine of claim 1 including means for electricallyheating each of the vacuum chambers.

4. The casting machine of claim 3 wherein the movable support is arotatable carriage and including a plurality of electrically conductiverings insulatingly mounted on said rotatable carriage, stationarybrushes adapted for connection to a source of electrical potential, andmeans electrically connecting the electrically conductive rings to themeans for electrically heating the vacuum chambers.

5. The casting machine of claim 1 wherein each of the vacuum chambersincludes a gate valve to which the first vacuum means is connectable atone of the index positions, and through which the resin system issealingly introduced into' the vacuum chamber at another of the indexpositions.

6. The casting machine of claim 1 wherein the plurality of indexpositions includes at least one position for unloading and loadingmolds, an index position at which said first vacuum means is connectableto provide a vacuum in the vacuum chambers, an index position at whichthe resin system is introduced while the vacuum is being maintained bythe second vacuum means, and an index position at which the vacuumchamber is brought back to atmospheric pressure.

7. The casting machine of claim 1 wherein the means for sealinglyintroducing the resin system into the vacuum chamber is evacuated tosubstantially the same pressure as the vacuum chamber which it is toservice.

8. The casting machine of claim 1 wherein the means for sealinglyintroducing the resin system into the vacuum chamber includes a sealablemixing chamber for mixing the materials of the resin system, heatingmeans for heating the materials to a predetermined temperature, vacuummeans for evacuating the mixing chamber, at least While the materialsare being mixed, and dispensing means for measuring and dispensing themixed resin system.

9. A casting machine for at least partially encapsulating electricalconductive means in a resin system, comprising:

a plurality of vacuum chambers each having sealable openings adapted forreceiving molds which contain the electrically conductive means to beencapsulated, and first valve means,

a first vacuum system connectable to the first valve means on saidvacuum chambers for providing a predetermined vacuum in each vacuumchamber after it has received a mold,

a plurality of second valve means,

a second vacuum system connected to said plurality of vacuum chambersthrough said plurality of second valve means, respectively, formaintaining the predetermined vacuum in the vacuum chamber provided bysaid first vacuum system, and

means adapted for sealingly introducing a resin system into a vacuumchamber through said first valve means, while the vacuum in the chamberis being maintained by said second vacuum system.

10. The casting machine of claim 9 including rotatable carriage means,and drive means for indexing said carriage means, with the plurality ofvacuum chambers being disposed on said carriage means.

11. The casting machine of claim 10 including a rotary vacuum shaft sealfor sealably connecting the second vacuum system to the plurality'ofvacuum chambers on the rotatable carriage means.

12. The casting machine of claim 11 including third valve means disposedon each of the plurality of vacuum chambers for bringing the vacuumchambers back to atmospheric pressure after the resin system has beenintroduced into the mold, and the second valve means has closed.

13. The casting machine of claim 12 wherein the drive means successivelyindexes the vacuum chambers through a plurality of index positions,including positions for unloading and loading molds, providing a vacuumwith the first vacuum system, introducing the resin system into the moldwhile the vacuum is being maintained by the second vacuum system, andreturning the vacuum chambers to atmospheric pressure with the thirdvalve means.

14. The casting machine of claim 9 wherein the means for sealinglyintroducing the resin system into the vacuum chamber is evacuated tosubstantially the same pressure as the vacuum chamber which it is toservice.

15. The casting machine of claim 9 wherein the means for sealinglyintroducing the resin system into the vacuum chambers includes asealable mixing chamber for mixing the materials of the resin system,heating means for heating the materials to a predetermined temperature,vacuum means for evacuating the mixing chamber, at least while thematerials are being mixed, and dispensing means for measuring anddispensing the mixed resin system.

References Cited UNITED STATES PATENTS 1,457,290 5/1923 Schroeder 18-201,900,456 3/1933 Mead 18-20 1,969,323 8/1934 Person 18-20' 2,414,5251/1947 Hill et a1 264-102 2,672,652 3/1954 Howe et a1. 1820 2,876,4923/1959 Frieder et al. 18-26 3,267,517 8/1966 Altermott 18-26 3,381,3395/1968 Trelease 1826 WILLIAM J. STEPHENSON, Primary Examiner U.S. Cl.X.R. 1820, 26

